This invention relates to vibration welding generally and more specifically to a technique to control vibration welding using the energy imparted to the parts by the vibration welder.
In the field of ultrasonic welding of plastic parts it is known to provide various modes of welding. One mode is based upon a time-based cycle wherein the ultrasonic weld is completed after a pre-selected time delay. In another mode a pre-selected load force between the plastic parts is employed. In a constant energy based cycle, the ultrasonic weld cycle continues until a pre-selected amount of energy, such as can be measured in watt-seconds, has been delivered to the plastic components.
Ultrasonic welding of plastic parts involves bringing plastic parts into pressurized contact with each other and while the parts are maintained in a stable physical relationship with each other, bringing an ultrasonic horn into contact with one of the plastic parts to inject ultrasonic energy into a small area immediately below the horn. The amount of ultrasonic energy imparted to the plastic pieces is sufficient to soften or melt the zones in alignment with the horn and thus enable the juxtaposed zones to fuse when the energy from the horn is no longer applied.
Vibration welding equipment generally bonds two plastic parts together by holding one part stationary and vibrating the other part while in contact at the bonding area under an applied force. This produces friction that melts the plastic at the joint area. When allowed to cool, the joint produced can be as strong as the surrounding material.
In vibration welding the plastic parts are pressed together by opposed platens, one of which is moved relative to the other so as to cause the frictional melting of contacting plastic surfaces. After melting, relative motion ceases to thus enable the surfaces to cool and fuse together. In vibration welding extended facing surfaces of the parts can be welded together in a short cycle, while ultrasonic welding of extended surfaces would involve a series of individual, either overlapping or spaced apart, spot welds.
In vibration welding control parameters typically involve either time, i.e. a fixed time period for completing the weld or distance, i.e. enabling the platens to move a fixed distance towards each other during the time that frictional melting under pressure occurs.
Vibration welding has been used for a wide variety of parts, including the automotive industry and supporting area such as engine components, door panels, intake manifolds, spoiler panels, filter housings and medical components. In many of these applications it is extremely critical to produce consistently strong bonds.
When a bond has not been properly produced for some unforeseen reason, it is equally important to identify and remove the suspect component from others that have been produced. Weld parameters of time, distance, pressure, hold time, vibration amplitude and variations of the part composition and its size can all have significant impact on the ability to produce a xe2x80x9cgoodxe2x80x9d weld.
With vibration welding equipment in accordance with the invention, the quality of a vibration weld is controlled by regulating the energy imparted to parts being welded together. This is achieved in accordance with one technique of the invention, by pre-selecting an energy set point and controlling the input power from the vibration welder until that energy set point has been reached during vibration welding.
An advantage of such energy control arises when, during the vibration welding process, an expected distance motion between the platen has not been achieved or has been exceeded. In such case, the vibration weld can be expected to be out of tolerance and a rejection of the part can be done for quality control.
Changes in values of any one of a variety of monitored parameters can indicate a change of the energy imparted to the parts during vibration welding and thus result in a quality control problem. When the correct amount of energy has not been delivered to weld the parts within the right amount of time, this information can be used to qualify a bond and reject the manufactured part or to accept the part.
It is, therefore, an object of the invention to provide a technique and system for monitoring the amount of energy imparted to work pieces in a vibration welder during a vibration welding operation to determine the quality of the vibration weld.
It is a further object of the invention to provide a technique and system for controlling the energy imparted into work pieces during a vibration welding operation.
These and other advantages and objects of the invention can be understood from the following detailed description of a preferred embodiment in accordance with the invention as described in conjunction with the drawings.